Re: [REGRESSION, bisect]cxgb4 port failure with TSO traffic after commit 10d3be569243def8("tcp-tso: do not split TSO packets at retransmit time")

[Eric Dumazet]

On Fri, 2016-06-24 at 07:25 -0700, Eric Dumazet wrote:
> Please do not top post on netdev mailing list
> 
> On Fri, Jun 24, 2016 at 4:38 AM, Arjun V. <ar...@chelsio.com> wrote:
> > Eric,
> > We are seeing skb's with length(skb->len) greater than 65536 coming into 
> > our ndo_start_xmit() callback routine.
> > We can add a check in our eth_xmit() routine to skip those packets, but it 
> > will be better if you fix this in kernel.
> >
> >
> > I have attached pcap file obtained from tcpdump. In the pcap file there are 
> > 2 such packets(I used tcpdump filter to extract out those packets).
> >
> > Let us know if you need anything else.
> >
> 
> Beats me really.
> 
> At retransmit time, we only can eventually reduce packet sizes
> (assuming GSO is used, because we might coalesce sub-mss packets in
> tcp_retrans_try_collapse())
> 
> So why are you seeing too big packets at retransmit, I really have no idea.
> 
> MIght be some bug related to MSS computation, overflowing somehow ?

Could you try this ?

Thanks !

diff --git a/net/ipv4/af_inet.c b/net/ipv4/af_inet.c
index 
d39e9e47a26e55ad2b8f775bf9ea9dfb5b12aee5..27013056bcfb9aa49601806bb3aa55a1ac664873
 100644
--- a/net/ipv4/af_inet.c
+++ b/net/ipv4/af_inet.c
@@ -1177,6 +1177,7 @@ int inet_sk_rebuild_header(struct sock *sk)
 
                /* Routing failed... */
                sk->sk_route_caps = 0;
+               sk->sk_gso_max_segs = 1;
                /*
                 * Other protocols have to map its equivalent state to 
TCP_SYN_SENT.
                 * DCCP maps its DCCP_REQUESTING state to TCP_SYN_SENT. -acme
diff --git a/net/ipv6/af_inet6.c b/net/ipv6/af_inet6.c
index 
2076c21107d07e4e78a0a29f1d374c3414b8e1bd..ecc0281acfb702b138c68ac51e3a0518052785b0
 100644
--- a/net/ipv6/af_inet6.c
+++ b/net/ipv6/af_inet6.c
@@ -685,6 +685,7 @@ int inet6_sk_rebuild_header(struct sock *sk)
                dst = ip6_dst_lookup_flow(sk, &fl6, final_p);
                if (IS_ERR(dst)) {
                        sk->sk_route_caps = 0;
+                       sk->sk_gso_max_segs = 1;
                        sk->sk_err_soft = -PTR_ERR(dst);
                        return PTR_ERR(dst);
                }